11.8.9 Anaesthesia for non-cardiac surgery

Pre-operative assessment

The presence of a rasping systolic murmur in the elderly is a common finding in the preoperative evaluation for non-cardiac surgery. Echocardiography confirms the diagnosis and specifies the degree of stenosis. This situation raises two important questions:

• Does aortic stenosis pose an excessive surgical risk ?
• If the stenosis is narrow (S < 0.6 cm²/m²  , ΔPmean > 40 mmHg), is AVR indicated before the planned operation?

If symptomatic (angina, syncope or dyspnoea) or associated with LV dilatation (Dtd > 4 cm²/m² ), a tight aortic stenosis should be corrected before any non-cardiac procedure [4,9]. The use of a bioprosthesis is preferred to avoid anticoagulation problems. Classically, only urgent, life-saving interventions that cannot be delayed can be considered in the presence of symptomatic tight stenosis, as their mortality is ≥ 10%, rising to 31% when more than three other comorbidities are present [4,5]. There are three possible scenarios for asymptomatic aortic stenosis (see Figure 11.31A) [2,3,9].

• The planned surgery is major (abdominal aortic surgery, hepato-pancreatic surgery, etc.); in this case, aortic valve replacement (AVR) is recommended before non-cardiac surgery.
• Planned surgery is moderate or minor: AVR is not justified. Although the cardiac morbidity is 15-25%, it is the same as in patients with mild to moderate stenosis. However, the more severe the stenosis, the greater the risk of intraoperative hypotension and the more tight the haemodynamic control.
• The presence of LV dysfunction worsens the prognosis and increases the indication for preoperative AVR, but this indication is essentially based on the long-term benefit to the patient, as AVR itself has a mortality of 2% under 70 and 5% over 75 [2].

AVR has its own risks and mortality (2-4%) [6]. If the predicted mortality of AVR is > 8-10%, it may be advisable to replace ECC procedure with transcatheter aortic valve implantation (TAVI) via the transapical or transfemoral route (see Chapter 10, Aortic valve implantation). Aortic valvuloplasty by balloon dilatation gives disappointing results for degenerative and/or calcified stenosis in older adults.

With advances in anaesthetic management based on rigorous haemodynamic control, recent comparative studies between patients with narrow aortic stenosis and those without stenosis tend to show that the results of non-cardiac surgery without prior AVR are acceptable, even if the risk is higher [1,8]. Patients with tight stenosis have more cardiac complications (18.8% versus 10.5%), mainly related to ventricular decompensation, but 30-day mortality is little changed compared to controls: symptomatic patients 5.9% versus 3.1%, asymptomatic patients 3.3% versus 2.7% [8]. These figures are superimposed on those for high-risk and intermediate-risk surgery in the general population. Given these good results, it is suggested that AVR be restricted to symptomatic patients (see Figure 11.31B). Intermediate and major non-cardiac surgery can be performed without undue risk in asymptomatic patients with narrow aortic stenosis. If the predicted mortality of AVR is greater than 8%, it may be preferable, depending on the risk, to proceed directly to non-cardiac surgery, taking care to ensure that anaesthesia is performed under invasive monitoring and strict haemodynamic control. TAVI itself carries an operative risk of 5-8% [6,7].

 Anaesthetic technique

Anaesthetic technique and monitoring should be based on the recommendations for cardiac anaesthesia.

• Slow induction with arterial catheter in place.
• Tolerance to IPPV assessed by Valsalva manoeuvre prior to induction.
• Monitoring:
  • Arterial catheter, ST segment monitoring.
  • TEE (LV function, blood volume) for major surgery with risk of hypovolaemia; TEE is the best tool for differential diagnosis of acute hypotension (hypovolaemia, LV dysfunction, ischaemia, HOCM).
  • Swan-Ganz: not very informative, dangerous (risk of arrhythmias and complete AV block).
• Induction agents:
  • Propofol (hypotension due to reduced preload).
  • Midazolam (hypotension due to reduced sympathetic tone, delayed awakening).
  • Etomidate (safest for high-risk cases).
  • Thiopental not recommended (hypotension and tachycardia).
  • Curare: avoid pancuronium (tachycardia).
  • Hypotension: alpha vasoconstrictors, avoid ephedrine.
• Maintenance of anaesthesia:
  • Halogenated: sevoflurane (preferred), desflurane (short procedures); isoflurane not recommended as it is too vasodilatory.
  • Propofol (infusion), midazolam (long procedures, late extubation)
  • IPPV with minimal PEEP (low mean Pit, preservation of venous return).
• Hypotension is more dangerous than hypertension (high ischaemic risk); maintain MAP ≥ 80 mmHg with vasoconstrictors (phenylephrine, noradrenaline).
• Inotropic support if required: dopamine (effects β + α ) or combination of dobutamine + noradrenaline (dobutamine alone: systemic vasodilatory effect).